It will be difficult to tell why the fever appeared only in sporadic cases in Philadelphia. Perhaps its prevalence as an epidemic was prevented by the plentiful rains in the spring months, by the absence of moisture from the filth of the streets and gutters, in consequence of the dry weather in June and July, by the vigour and perfection of the products of the earth, and by the variable state of the winds in the month of July. If none of these causes defended the city from more numerous cases of the yellow fever, it must be resolved into the want of a concurring inflammatory constitution of the atmosphere with the common impure sources of that disease. On the 12th of November, about twelve o'clock in the night, an earthquake was felt in Philadelphia, attended with a noise as if something heavy had fallen upon a floor. Several cases of scarlet fever appeared in December, but the prevailing disease, during the two last autumnal and the first winter months, was the measles. I have taken notice that it appeared in the south end of the city in July. During the months of August and September it was stationary, but in October, November, and December it spread through every part of the city. The following circumstances occurred in this epidemic, as far as it came under my notice. AN ACCOUNT OF THE MEASLES, AS THEY APPEARED IN PHILADELPHIA, IN THE YEAR 1801. I. The disease wore the livery of the autumnal fever in the following particulars. It was strongly marked by remissions and intermissions. The exacerbations came on chiefly at night. There were in many cases a constant nausea, and discharge of bile by puking. I saw one case in which the disease appeared with a violent cholera morbus, and several in which it was accompanied with diarrh[oe]a and dysentery. II. Many severe cases of phrenzy, and two of cynanche trachealis appeared with the measles. III. A distressing sore mouth followed them, in a child of two years old, that came under my care. IV. A fatal hydrocephalus internus followed them in a boy of eight years old, whom I saw two days before he died. V. I met with a few cases in which the fever and eruption came on in the same day, but I saw one case in which the eruption did not take place until the tenth, and another, in which it did not appear until the fourteenth day after the fever. VI. Two children had pustules on their skins, resembling the small-pox, before the eruption of the measles. VII. Many children had coughs and watery eyes, but without the measles. The same children had them two or three weeks afterwards. VIII. Many people who had had the measles, had coughs during the prevalence of the measles, resembling the cough which occurs in that disease. The remedies made use of in my practice were,